The court shall determine custody in accordance with the best interest of the child. The court determines custody based upon a series of factors set forth in A.R.S. § 25-403(A). These factors include:

The wishes of the child's parent or parents as to custody. The wishes of the child as to the custodian. The interaction and interrelationship of the child with the child's parent or parents, the child's siblings and any other person who may significantly affect the child's best interest. The child's adjustment to home, school and community. The mental and physical health of all individuals involved. Which parent is more likely to allow the child frequent and meaningful continuing contact with the other parent. Whether one parent, both parents or neither parent has provided primary care of the child. The nature and extent of coercion or duress used by a parent in obtaining an agreement regarding custody. Whether a parent has complied with chapter 3, article 5 of this title. [The Parent Information Program] Whether either parent was convicted of an act of false reporting of child abuse or neglect under A.R.S. § 13-2907.02.

The court is not to prefer either parent because of the parent's sex. There is no presumption favoring either sole custody or joint custody. Before awarding custody the court may interview the child in chambers, and the court may seek professional advice. Such advice shall be made available to counsel by the court when requested. The court may also order an investigation. The mental health of every individual involved is relevant in a custody proceeding. A.R.S. § 25-403.